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Methods for fabrication of thermal interposers, using a low stress
photopatternable silicone are provided, for use in production of
electronic products that feed into packaging of LEDs, logic and memory
devices and other such semiconductor products where thermal management is
desired. A photopatternable silicone composition, thermally conductive
material and a low melting point compliant solder form a complete
semiconductor package module. The photopatternable silicone is applied on
a surface of a wafer and selectively radiated to form openings which
provided user defined bondline thickness control. The openings are then
filled with high conductivity pastes to form high conductivity thermal
links. A low melting point curable solder is then applied where the
solder wets the silicone as well as the thermally conductive path that
leads to low thermal contact resistance between the structured z-axis
thermal interposer and the heat sink and/or substrate which can be a
wafer or PCB.

1) A method of forming a thermally conductive interposer on a wafer, the
method comprising the step of filling a plurality of apertures in a cured
layer formed on a surface of the wafer, with a thermally conductive
material to form the thermally conductive interposer.

2) The method of claim 1, wherein the thickness of the cured layer
corresponds to a z-axis thickness and the apertures are through the cured
layer along the z-axis thickness.

3) The method of claim 1, wherein the cured layer is a product of
photopatterning and curing a layer of a photopatternable silicone
composition comprising: A) an organopolysiloxane containing an average of
at least two silicon-bonded alkenyl groups per molecule, B) an
organosilicon compound containing an average of at least two
silicon-bonded hydrogen atoms per molecule in a concentration sufficient
to cure the composition, and C) a catalytic amount of a photoactivated
hydrosilylation catalyst.

4) The method of claim 3, which includes the step of applying a mixture
of the photopatternable silicone composition and a solvent to at least
one surface of the wafer to form an applied layer covering at least a
portion of the surface of the wafer; photopatterning the applied layer;
and curing the photopatterned applied layer.

5) The method of claim 4, which includes the steps of: i) irradiating a
portion of the applied layer with a radiation including an i-line
radiation, while masking another portion of the applied layer, to produce
a partially-irradiated layer having non-irradiated regions covering at
least a portion of the surface of the wafer and irradiated regions
covering the remainder of the surface of the wafer; ii) partially curing
the irradiated applied layer by heat; iii) removing the non-irradiated
regions of the partially cured layer with a developing solvent to form a
partially cured layer with a plurality of z-axis apertures defined
therein; and iv) curing the partially cured layer to give the cured
layer.

6) The method of claim 5, wherein the radiation is ultraviolet (UV)
radiation and intensity of the UV radiation is in the range from 800
millijoules per square centimeter (mJ/cm.sup.2) to 2800 mJ/cm.sup.2; or
wherein the irradiated applied layer is partially cured by heating the
layer to a temperature in the range from 100 degrees Celsius (.degree.
C.) to 150.degree. C. for from 2 minutes to 5 minutes; or wherein the
step of removing the non-irradiated regions is carried out by immersing
the partially cured layer in the developing solvent selected from the
group consisting of butyl acetate and mesitylene; or wherein the
partially cured layer is cured by heating the partially cured layer to a
temperature in the range from 180 degrees Celsius (.degree. C.) to
400.degree. C. for from 30 minutes to 3 hours.

7) The method of claim 4, further comprising, after the step of applying
the photopatternable silicone composition, the step of removing at least
a portion of the solvent from the applied layer by heating the applied
layer to a temperature in the range from 50 degrees Celsius (.degree. C.)
to 130.degree. C. for 2 minutes to 5 minutes.

8) The method of claim 1, wherein the thermally conductive material is
selected from the group consisting of titanium; aluminum; nickel; copper;
silver; gold; alloys of any two or more of titanium, aluminum, nickel,
copper, silver, and gold; carbon, boron nitride; carbon nanotubes; and
combinations of any two or more thereof.

9) A thermally conductive interposer for dissipating heat from a wafer,
the interposer covering at least one surface of the wafer, the interposer
is composed of a cured layer having a pattern of a thermally conductive
material disposed at discrete locations therein, wherein the cured layer
is a product of photopatterning and curing a layer of a photopatternable
silicone composition comprising: A) an organopolysiloxane containing an
average of at least two silicon-bonded alkenyl groups per molecule, B) an
organosilicon compound containing an average of at least two
silicon-bonded hydrogen atoms per molecule in a concentration sufficient
to cure the composition, and C) a catalytic amount of a photoactivated
hydrosilylation catalyst; the interposer defining a plurality of
apertures at pre-determined locations within the interposer, wherein at
least some of the apertures having the thermally conductive material
disposed therein.

10) A thermally conductive interposer as prepared by the method of claim
1.

11) The thermally conductive interposer of claim 10, wherein at least
some of the apertures are z-axis vias.

12) A method of making a semiconductor package, the method comprising the
following steps: i) Filling, with thermally conductive material a
plurality of apertures in a cured layer formed on a surface of a wafer,
to form a thermally conductive interposer on the wafer; ii) dicing the
wafer to produce individual diced wafers with the thermally conductive
interposer formed thereon; iii) placing each diced wafer in the proximity
of a substrate such that the thermally conductive interposer of each
diced wafer faces the substrate; iv) placing a bead or layer of solder
between each filled aperture in the interposer and the substrate; and v)
melting the solder to form a bond between thermally conductive material
in the aperture and the substrate.

13) The method of claim 12, wherein the thickness of the cured layer
corresponds to a z-axis thickness and the apertures are through the cured
layer along the z-axis thickness.

14) The method of claim 12, wherein the cured layer is a product of
photopatterning and curing a layer of a photopatternable silicone
composition comprising: A) an organopolysiloxane containing an average of
at least two silicon-bonded alkenyl groups per molecule, B) an
organosilicon compound containing an average of at least two
silicon-bonded hydrogen atoms per molecule in a concentration sufficient
to cure the composition, and C) a catalytic amount of a photoactivated
hydrosilylation catalyst.

15) A semiconductor package comprising: i) a wafer comprising at least
one surface; ii) a thermally conductive interposer covering the surface
of the wafer for dissipating heat from the wafer, the interposer defining
a plurality of apertures defined at pre-determined locations within the
interposer, at least some of the apertures having thermally conductive
material disposed therein, the interposer composed of a cured layer,
wherein the cured layer is a product of photopatterning and curing a
layer of a photopatternable silicone composition comprising: A) an
organopolysiloxane containing an average of at least two silicon-bonded
alkenyl groups per molecule, B) an organosilicon compound containing an
average of at least two silicon-bonded hydrogen atoms per molecule in a
concentration sufficient to cure the composition, and C) a catalytic
amount of a photoactivated hydrosilylation catalyst; iii) a semiconductor
package substrate; and iv) a bead or layer of solder dispensed between
each filled aperture in the interposer and the substrate to form a bond
between thermally conductive material in the aperture and the substrate.

[0002] Semiconductor devices are becoming smaller and more powerful.
Semiconductor devices with high operating frequencies and large numbers
of components with complex circuit densities are being fabricated with
smaller packages, leading to increasing thermal challenges. High
operating frequencies increase power consumption and consequently heat
generation in a semiconductor device package. Typically, cooling hardware
such as fans and heat sinks are used to dissipate the heat generated by
the semiconductor device and cool the device. However, transfer of heat
from the hot components in the semiconductor device package to the
cooling hardware is may also be provided to significantly cool the
semiconductor device.

[0003] Thermal Interface Materials (TIMs) are typically used as heat
transport media between active semiconductor wafers/dies and substrates
or heat sinks, to enhance the heat transport between the active die and
heat sink. Gels, greases and adhesives filled with metal particles are
used as TIMs for die to substrate, die to lid and/or die to heat sink
attachment. Typical thermal conductivity values of the TIMs range from 1
to several Watts per meter-Kelvin (Wm.sup.-1K.sup.-1) depending on the
filler type, size distribution, loading and starting matrix. General
method of applying a TIM involves dispensing of the TIM material after
the die is diced and bonded to an active die or substrate. The methods of
applying TIMs are well known in the art. However, hitherto applications
of TIMs take place on die levels, thereby limiting the use of TIMs. The
term "die level" means that the application of TIM and assembly of the
die happens after the processed wafer is diced into individual dies.

[0004] The TIM materials used for heat transport are made of insulative
matrices such as epoxies or silicones which are filled with thermal
conductive particles such as alumina, silver or gold for better thermal
conduction. Thus the composite matrix of the filled TIM has a thermal
conductivity closer to that of the insulative matrix rather than that of
the fillers. For instance, the thermal conductivity of a typical silicone
is 0.2-0.3 W m.sup.-1K.sup.-1, and when such a silicone is filled with
silver particles whose thermal conductivity is 429 Wm.sup.-1K.sup.-1, the
thermal conductivity of the silicone-silver composite is approximately
2-3 Wm.sup.-1K.sup.-1. Thus there is a general limitation on the
effectiveness of TIMs as a heat transport medium.

[0005] Furthermore, the use of fillers in TIMs makes desirable careful
management of the filler technology to prevent settling of fillers, as
well as proper handling and dispensing of filled composites, forming
uniform bond lines, and the like. These considerations further complicate
the task of making a reliable low cost semiconductor device package
module. Typically, the reverse side of most active semiconductor devices
are rough, leading to air pockets and high thermal contact resistance
between the TIM and the device thus reducing the effectiveness of the
TIM.

[0006] Silicon interposers are being increasingly used as the heat
transport medium within the semiconductor device package. Silicon
interposers are typically passive silicon substrates or dies having
through-silicon-vias that are used to interconnect active dies without
the need to specifically design the dies for interface compatibility.
Silicon interposers are used to stack active dies side-by-side and/or
vertically in a package.

[0007] There have been endeavors to develop silicon interposers as heat
transport mediums within the semiconductor device packages. For instance,
U.S. patent application publication no. US20050280128 recites a thermal
interposer provided for attachment to a surface of a semiconductor
device. The interposer includes an upper plate and a lower plate
hermetically bonded together. The use of two plates and the hermetic
bonding of the two plates make the interposer complex to manufacture.
Furthermore, precise bonding of the two plates is desired for efficient
functioning of the interposer.

[0008] U.S. patent application publication no. US20060006526 mentions a
multilayered thermal interposer having two conductors bonded to an
insulating layer with a bonding layer. However, the multiple layers of
the thermal interposer make the manufacturing of the interposer and the
semiconductor device package more complex.

[0009] U.S. patent application publication no. US20100044856 mentions an
electronic package having a die including a thermal interface material
for conducting heat from the die, an organic substrate, and a thermal
interposer provided between the organic substrate and the die. The area
of the thermal interposer extends beyond a footprint of the die and
includes the thermal interface material. The thermal interposer conducts
heat generated by the die through the thermal interface material.
However, to accommodate additional area of the thermal interposer that
extends beyond the footprint of the die, a bigger semiconductor device
package is desired, thus limiting the use of the thermal interposer and
rendering the thermal interposer unusable when fabricating smaller
packages.

[0011] WO2012/142592 recites a silicon interposer with through package
vias. The silicon interposer comprises a silicon substrate in panel or
wafer form having through package vias defined therein and redistribution
layers on first and second sides of the silicon substrate simultaneously.
However, the silicon interposer of WO2012/142592 is designed to reduce
electrical losses within a semiconductor package thereby necessitating
the use of a silicon wafer as the interposer. Moreover, the method of
making the silicon interposer involves drilling or laser ablation of the
wafer to create through package vias within the silicon wafer and further
forming polymeric liners within the through package vias.

[0012] With the advent of 3-dimensional (3D) and 2.5D stacked memory and
logic modules it is important to create architectures which are efficient
mediums for thermal transport. Thus there is a need for newer more
efficient methods of thermal management which allows for well controlled
thin bond lines, low thermal contact resistances, high thermal
conductivity and adaptability for large scale manufacturing.

BRIEF SUMMARY OF THE INVENTION

[0013] The present disclosure is directed to methods of using a silicone
composition to form thermally conductive interposers in semiconductor
device packages for efficient thermal management. In accordance with an
aspect of the present disclosure, there is provided a method of forming a
thermally conductive interposer on a wafer. The method comprising filling
a plurality of apertures in a cured layer formed on a surface of the
wafer, with thermally conductive material to form the thermally
conductive interposer on the wafer.

[0014] In accordance with another aspect of the present disclosure, there
is provided a thermally conductive interposer for dissipating heat from a
wafer. The interposer covers at least one surface of the wafer, the
interposer is composed of a cured layer having a pattern of thermally
conductive material disposed at discrete locations therein, wherein the
cured layer is a product of photopatterning and curing a layer of a
photopatternable silicone (PPS) composition comprising: (A) an
organopolysiloxane containing an average of at least two silicon-bonded
alkenyl groups per molecule, (B) an organosilicon compound containing an
average of at least two silicon-bonded hydrogen atoms per molecule in a
concentration sufficient to cure the composition, and (C) a catalytic
amount of a photoactivated hydrosilylation catalyst. The interposer
defines a plurality of apertures defined at pre-determined locations
within the interposer, wherein at least some of the apertures have a
thermally conductive material disposed therein.

[0015] In accordance with yet another aspect of the present disclosure,
there is provided a method of preparing a semiconductor package. The
method comprises filling a plurality of apertures in a cured layer formed
on a surface of a wafer, with thermally conductive material to form a
thermally conductive interposer on the wafer. The method further
comprises depositing a layer of solder on the thermally conductive
interposer. The method further comprises dicing the wafer to produce
individual diced wafers with the thermally conductive interposer and the
layer of solder formed thereon. The method further comprises placing each
diced wafer in the proximity of a semiconductor package lid/heat sink
such that the thermally conductive interposer of each diced wafer having
the layer of solder thereon faces the heat sink and melting the solder to
form a bond between thermally conductive material in the aperture and the
heat sink.

[0016] In accordance with still another aspect of the present disclosure,
there is provided a semiconductor package. The semiconductor package
comprises a wafer comprising at least one surface; a thermally conductive
interposer covering the surface of the wafer for dissipating heat from
the wafer, wherein the interposer defines a plurality of apertures
defined at pre-determined locations within the interposer, with at least
some of the apertures having thermally conductive material disposed
therein; a semiconductor package substrate; and a layer of solder
dispensed between each filled aperture in the interposer and a
semiconductor package lid/heat sink to form a bond between thermally
conductive material in the aperture and the heat sink. The interposer is
composed of a cured layer, wherein the cured layer is a product of
photopatterning and curing a layer of a photopatternable silicone
composition comprising: A) an organopolysiloxane containing an average of
at least two silicon-bonded alkenyl groups per molecule, B) an
organosilicon compound containing an average of at least two
silicon-bonded hydrogen atoms per molecule in a concentration sufficient
to cure the composition, and C) a catalytic amount of a photoactivated
hydrosilylation catalyst.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

[0017] Various advantages of the invention will become apparent upon
reading the following detailed description and upon reference to the
accompanying drawings.

[0019] FIG. 2 shows a schematic representation of the process steps
involved in the fabrication of an electronic package with a
photopatternable silicone composition based Z-axis thickness thermal
interposer at wafer level.

[0022] FIG. 5 shows a flow chart depicting the steps involved in the
method of forming the thermally conductive interposer in accordance with
additional exemplary embodiments.

[0023] While the invention is susceptible to various modifications and
alternative forms, specific embodiments have been shown by way of example
in the drawings and will be described in detail herein, and the invention
is not intended to be limited to the particular forms disclosed.

DETAILED DESCRIPTION OF THE INVENTION

[0024] As used herein, "may" confers a choice, not an imperative.
"Optionally" means is absent, alternatively is present. "Contacting"
means bringing into physical contact. "Operative contact" comprises
functionally effective touching, e.g., as for modifying, coating,
adhering, sealing, or filling. The operative contact may be direct
physical touching, alternatively indirect touching. All U.S. patent
application publications and patents referenced herein, or a portion
thereof if only the portion is referenced, are hereby incorporated herein
by reference to the extent that incorporated subject matter does not
conflict with the present description, which would control in any such
conflict. All states of matter are determined at 25.degree. C. and 101.3
kPa unless indicated otherwise. All % are by weight unless otherwise
noted. All wt % values are, unless otherwise noted, based on total weight
of all ingredients used to synthesize or make the composition, which adds
up to 100 wt %. Any Markush group comprising a genus and subgenus therein
includes the subgenus in the genus, e.g., in "R is hydrocarbyl or
alkenyl," R may be alkenyl, alternatively R may be hydrocarbyl, which
includes, among other subgenuses, alkenyl.

[0025] In accordance with an aspect of this invention a photopatternable
silicone composition can be used to form a thermally conductive
interposer on a wafer. Such use of a photopatternable silicone may enable
end users to apply the silicone on semiconductor wafers as desired,
pattern and develop/remove areas of the silicone wherein thermally
conductive material is to be deposited, thus giving the users flexibility
to design the location of the apertures closer to areas in need of higher
heat dissipation. Furthermore, this aspect of the invention eliminates
the need for the prior art filler technology mentioned earlier, thereby
reducing the cost and complexity associated with filler management and
homogeneously dispensing high viscosity filled TIMs. The aspect also
provides good bond line thickness control and reduces the need for
managing thermal contact resistance associated with filled TIMs. The term
"bond lie" refers to the gap between the die and the heat sink which is
defined by the thickness of the photopatternable silicone composition and
the layer of solder applied onto the wafer.

[0026] The thermally conductive interposer may be formed at wafer level
with thermal apertures/vias which may be of uniform thickness and/or
width, alternatively of varying thickness and width thereby providing
flexibility in design of via structures and locations and giving users
the flexibility to locate the apertures at or close to "hot spots" on the
die to dissipate heat from the die. The term "wafer level" means that the
thermally conductive interposer is formed on a whole wafer before the
wafer is diced into individual dies. Furthermore, this aspect can
eliminate the need for handling and dispensing of thermal interface
composite materials on the die level thus reducing the cost.
Additionally, the photopatternable silicone acts as a stress buffer which
enables the management of stress on active devices which are primarily
composed of materials with different CTE (Coefficients of Thermal
Expansion), thus helping to increase the reliability of the thermally
conductive interposer and the devices.

[0027] The photopatternable silicone composition may be composed of three
primary components and additional secondary components described in U.S.
Pat. No. 7,517,808 which is hereby incorporated by reference. The primary
components of photopatternable silicone composition include, (A) an
organopolysiloxane containing an average of at least two silicon-bonded
alkenyl groups per molecule, (B) an organosilicon compound containing an
average of at least two silicon-bonded hydrogen atoms per molecule in a
concentration sufficient to cure the composition, and (C) a catalytic
amount of a photoactivated hydrosilylation catalyst.

[0028] Component (A) is at least one organopolysiloxane containing an
average of at least two silicon-bonded alkenyl groups per molecule. The
organopolysiloxane can have a linear, branched, or resinous structure.
The organopolysiloxane can be a homopolymer or a copolymer. The alkenyl
groups typically have from 2 to about 10 carbon atoms and are exemplified
by, but not limited to, vinyl, allyl, butenyl, and hexenyl. The alkenyl
groups in the organopolysiloxane may be located at terminal, pendant, or
both terminal and pendant positions. The remaining silicon-bonded organic
groups in the organopolysiloxane are independently selected from
monovalent hydrocarbon and monovalent halogenated hydrocarbon groups free
of aliphatic unsaturation. These monovalent groups typically have from 1
to about 20 carbon atoms, alternatively have from 1 to 10 carbon atoms,
and are exemplified by, but not limited to alkyl such as methyl, ethyl,
propyl, pentyl, octyl, undecyl, and octadecyl; cycloalkyl such as
cyclohexyl; aryl such as phenyl, tolyl, xylyl, benzyl, and 2-phenylethyl;
and halogenated hydrocarbon groups such as 3,3,3-trifluoropropyl,
3-chloropropyl, and dichlorophenyl. At least 50 percent, and
alternatively at least 80%, of the organic groups free of aliphatic
unsaturation in the organopolysiloxane can be methyl.

[0029] The viscosity of the organopolysiloxane at 25.degree. C. is
typically from 0.001 to 100,000 Pas, alternatively from 0.01 to 10,000
Pas, and alternatively from 0.01 to 1,000 Pas.

[0030] Examples of organopolysiloxanes useful as component (A) in the
photopatternable silicone composition include, but are not limited to,
polydiorganosiloxanes having the following formulae:
ViMe.sub.2SiO(Me.sub.2SiO).sub.aSiMe.sub.2Vi,
ViMe.sub.2SiO(Me.sub.2SiO).sub.0.25a(MePhSiO).sub.0.75aSiMe.sub.2Vi,
ViMe.sub.2SiO(Me.sub.2SiO).sub.0.95a(Ph.sub.2SiO).sub.0.05aSiMe.sub.2Vi,
ViMe.sub.2SiO(Me.sub.2SiO).sub.0.98a(MeViSiO).sub.0.02aSiMe.sub.2Vi,
Me.sub.3SiO(Me.sub.2SiO).sub.0.95a(MeViSiO).sub.0.05aSiMe.sub.3, and
PhMeViSiO(Me.sub.2SiO).sub.aSiPhMeVi, where Me, Vi, and Ph denote methyl,
vinyl, and phenyl respectively and a has a value such that the viscosity
of the polydiorganosiloxane is from 0.001 to 100,000 Pas. at 25.degree.
C.

[0031] Methods of preparing organopolysiloxanes suitable for use in the
photopatternable silicone composition, such as methods comprising
hydrolysis and condensation of the corresponding organohalosilanes or
equilibration of cyclic polydiorganosiloxanes, are well known in the art.

[0032] The organopolysiloxane of component (A) may be an
organopolysiloxane resin. Examples of suitable organopolysiloxane resins
include an MQ resin comprising R.sup.1.sub.3SiO.sub.1/2 units and
SiO.sub.4/2 units, a TD resins comprising R.sup.1SiO.sub.3/2 units and
R.sup.1.sub.2SiO.sub.2/2 units, an MT resin comprising
R.sup.1.sub.3SiO.sub.1/2 units and R.sup.1SiO.sub.3/2 units, and an MTD
resin comprising R.sup.1.sub.3SiO.sub.1/2 units, R.sup.1SiO.sub.3/2
units, and R.sup.1.sub.2SiO.sub.2/2 units, wherein each R.sup.1 is
independently selected from monovalent hydrocarbon and monovalent
halogenated hydrocarbon groups. The monovalent groups represented by
R.sup.1 typically have from 1 to about 20 carbon atoms and alternatively
have from 1 to about 10 carbon atoms. Examples of monovalent groups
include, but are not limited to, alkyl such as methyl, ethyl, propyl,
pentyl, octyl, undecyl, and octadecyl; cycloalkyl such as cyclohexyl;
alkenyl such as vinyl, allyl, butenyl, and hexenyl; aryl such as phenyl,
tolyl, xylyl, benzyl, and 2-phenylethyl; and halogenated hydrocarbon
groups such as 3,3,3-trifluoropropyl, 3-chloropropyl, and dichlorophenyl.
At least one-third, and alternatively substantially all R.sup.1 groups in
the organopolysiloxane resin may be methyl. A typical organopolysiloxane
resin may be an MQ resin, which comprises (CH.sub.3).sub.3SiO.sub.1/2
siloxane units and SiO.sub.4/2 units, wherein the mole ratio of
(CH.sub.3).sub.3SiO.sub.1/2 units to SiO.sub.4/2 units is from 0.6 to
1.9.

[0033] The organopolysiloxane resin may contain an average of about 3 to
30 mole percent of alkenyl groups. The mole percent of alkenyl groups in
the resin is defined here as the ratio of the number of moles of
alkenyl-containing siloxane units in the resin to the total number of
moles of siloxane units in the resin, multiplied by 100.

[0034] The organopolysiloxane resin can be obtained from commercial
sources or can be prepared by methods well-known in the art. The resin
may be prepared by treating a resin copolymer produced by the silica
hydrosol capping process of Daudt et al. with at least an
alkenyl-containing endblocking reagent. The method of Daudt et al. is
disclosed in U.S. Pat. No. 2,676,182, which is hereby incorporated by
reference to teach how to make organopolysiloxane resins suitable for use
in the present invention.

[0035] Briefly stated, the method of Daudt et al. involves reacting a
silica hydrosol under acidic conditions with a hydrolyzable
triorganosilane such as trimethylchlorosilane, a siloxane such as
hexamethyldisiloxane, or combinations thereof, and recovering a copolymer
having M and Q units. The resulting copolymer product generally contains
from about 2 to about 5 percent by weight of silicon-bonded hydroxyl
groups (Si--OH groups).

[0036] A organopolysiloxane resin, which typically contains less than 2
percent by weight of silicon-bonded hydroxyl groups, can be prepared by
reacting the copolymer product of Daudt et al. with an alkenyl-containing
endblocking agent or a combination of an alkenyl-containing endblocking
agent and an endblocking agent free of aliphatic unsaturation in an
amount sufficient to provide from 3 to 30 mole percent of alkenyl groups
and less than 2 percent by weight of silicon-bonded hydroxyl groups in
the final organopolysiloxane resin. Examples of such endblocking agents
include, but are not limited to, silazanes, siloxanes, and silanes.
Suitable endblocking agents are known in the art and exemplified in U.S.
Pat. No. 4,584,355 to Blizzard et al.; U.S. Pat. No. 4,591,622 to
Blizzard et al.; and U.S. Pat. No. 4,585,836 to Homan et al.; which are
hereby incorporated by reference. A single endblocking agent or a
combination of such agents can be used to prepare the organopolysiloxane
resin.

[0037] Component (A) can be a single organopolysiloxane or a combination
comprising two or more organopolysiloxanes that differ in at least one of
the following properties: structure, viscosity, average molecular weight,
siloxane units, and sequence.

[0038] Component (B) is at least one organosilicon compound containing an
average of at least two silicon-bonded hydrogen atoms per molecule. It is
generally understood that crosslinking in the photopatternable silicone
composition may occur when the sum of the average number of alkenyl
groups per molecule in component (A) and the average number of
silicon-bonded hydrogen atoms per molecule in component (B) is greater
than four. The silicon-bonded hydrogen atoms in the
organohydrogenpolysiloxane can be located at terminal, pendant, or at
both terminal and pendant positions.

[0039] The organosilicon compound containing an average of at least two
silicon-bonded hydrogen atoms per molecule can be an organosilane or an
organohydrogensiloxane. The organosilane can be a monosilane, disilane,
trisilane, or polysilane. Similarly, the organohydrogensiloxane can be a
disiloxane, trisiloxane, or polysiloxane. The organosilicon compound may
be the organohydrogensiloxane. The structure of the organosilicon
compound can be linear, branched, cyclic, or resinous. At least 50
percent of the organic groups in the organosilicon compound may be
methyl.

[0040] Examples of organosilanes suitable for use as component (B)
include, but are not limited to, monosilanes such as diphenylsilane and
2-chloroethylsilane; disilanes such as 1,4-bis(dimethylsilyl)benzene,
bis[(p-dimethylsilyl)phenyl]ether, and 1,4-dimethyldisilylethane;
trisilanes such as 1,3,5-tris(dimethylsilyl)benzene and
1,3,5-trimethyl-1,3,5-trisilane; and polysilanes such as
poly(methylsilylene)phenylene and poly(methylsilylene)methylene.

[0041] Examples of organohydrogensiloxanes suitable for use as component
(B) include, but are not limited to, disiloxanes such as
1,1,3,3-tetramethyldisiloxane and 1,1,3,3-tetraphenyldisiloxane;
trisiloxanes such as phenyltris(dimethylsiloxy)silane and
1,3,5-trimethylcyclotrisiloxane; and polysiloxanes such as a
trimethylsiloxy-terminated poly(methylhydrogensiloxane), a
trimethylsiloxy-terminated poly(dimethylsiloxane/methylhydrogensiloxane),
a dimethylhydrogensiloxy-terminated poly(methylhydrogensiloxane), and a
resin comprising H(CH.sub.3).sub.2SiO.sub.1/2 units,
(CH.sub.3).sub.3SiO.sub.1/2 units, and SiO.sub.4/2 units.

[0042] Component (B) can be a single organosilicon compound containing an
average of at least two silicon-bonded hydrogen atoms per molecule or a
combination comprising two or more such compounds that differ in at least
one of the following properties: structure, average molecular weight,
viscosity, silane units, siloxane units, and sequence.

[0043] The concentration of component (B) in the photopatternable silicone
composition is sufficient to cure, alternatively cure and crosslink, the
composition. The exact amount of component (B) depends on the desired
extent of cure, which generally increases as the ratio of the number of
moles of silicon-bonded hydrogen atoms in component (B) to the number of
moles of alkenyl groups in component (A) increases. Typically, the
concentration of component (B) is sufficient to provide from 0.5 to 3
silicon-bonded hydrogen atoms per alkenyl group in component (A). The
concentration of component (B) may be sufficient to provide from 0.7 to
1.2 silicon-bonded hydrogen atoms per alkenyl group in component (A).

[0044] Methods of preparing organosilicon compounds containing an average
of at least two silicon-bonded hydrogen atoms per molecule are well known
in the art. For example, organopolysilanes can be prepared by reaction of
chlorosilanes in a hydrocarbon solvent in the presence of sodium or
lithium metal (Wurtz reaction). Organopolysiloxanes can be prepared by
hydrolysis and condensation of organohalosilanes.

[0045] To ensure compatibility of components (A) and (B), the predominant
organic group in each component may be the same. This group may be
methyl.

[0046] Component (C) is a photoactivated hydrosilylation catalyst. The
photoactivated hydrosilylation catalyst can be any hydrosilylation
catalyst capable of catalyzing the hydrosilylation of component (A) with
component (B) upon exposure to radiation having a wavelength of 150 to
800 nm and subsequent heating. Component (C) may be a platinum group
metal. Suitable platinum group metals include platinum, rhodium,
ruthenium, palladium, osmium and iridium. The component (C) may be
platinum, based on its high activity in hydrosilylation reactions. The
suitability of particular photoactivated hydrosilylation catalyst for use
in the photopatternable silicone composition can be readily determined by
routine experimentation using the methods in the Examples section below.

[0048] Component (C) can be a single photoactivated hydrosilylation
catalyst or a combination comprising two or more such catalysts.

[0049] The concentration of component (C) in the photopatternable silicone
composition is sufficient to catalyze the addition reaction of components
(A) and (B) upon exposure to radiation and heat in the method described
below. The concentration of component (C) is sufficient to provide
typically from 0.1 to 1000 ppm of platinum group metal, alternatively
from 0.5 to 100 ppm of platinum group metal, and alternatively from 1 to
25 ppm of platinum group metal, based on the combined weight of
components (A), (B), and (C). The rate of cure typically is very slow
below 1 ppm of platinum group metal. The use of more than 100 ppm of
platinum group metal may result in no appreciable increase in cure rate,
and is therefore uneconomical.

[0050] Methods of preparing the preceding photoactivated hydrosilylation
catalysts of component (C) are well known in the art. For example,
methods of preparing platinum(II) .beta.-diketonates are reported by Guo
et al. (Chemistry of Materials, 1998, 10, 531-536). Methods of preparing
(.eta.-cyclopentadienyl)trialkylplatinum complexes and are disclosed in
U.S. Pat. No. 4,510,094. Methods of preparing triazene oxide-transition
metal complexes are disclosed in U.S. Pat. No. 5,496,961. And, methods of
preparing (.eta.-diolefin)(.sigma.-aryl)platinum complexes are disclosed
in U.S. Pat. No. 4,530,879.

[0051] Combinations of the aforementioned components (A), (B), and (C) may
begin to cure at ambient temperature, typically from 20.degree. to
25.degree. C. To obtain a longer working time or "pot life", the activity
of the catalyst under ambient conditions can be inhibited, retarded or
suppressed by the addition of a suitable catalyst inhibitor to the
component (C) of the photopatternable silicone composition. A catalyst
inhibitor retards curing of the photopatternable silicone composition at
ambient temperature, but does not prevent the composition from curing at
elevated temperatures, typically from 30.degree. to 150.degree. C.
Suitable catalyst inhibitors include various "ene-yne" systems such as
3-methyl-3-penten-1-yne and 3,5-dimethyl-3-hexen-1-yne; acetylenic
alcohols such as 3,5-dimethyl-1-hexyn-3-ol, 1-ethynyl-1-cyclohexanol, and
2-phenyl-3-butyn-2-ol; maleates and fumarates, such as the well-known
dialkyl, dialkenyl, and dialkoxyalkyl fumarates and maleates; and
cyclovinylsiloxanes. Acetylenic alcohols constitute a typical class of
catalyst inhibitors that may be used in the photopatternable silicone
composition.

[0052] The concentration of the catalyst inhibitor in the photopatternable
silicone composition can be sufficient to retard curing of the
composition at ambient temperature without preventing or excessively
prolonging cure at elevated temperatures. This concentration can vary
widely depending on the particular inhibitor used, the nature and
concentration of the hydrosilylation catalyst, and the nature of the
organohydrogenpolysiloxane.

[0053] Catalyst inhibitor concentrations as low as one mole of inhibitor
per mole of platinum group metal will in some instances yield a
satisfactory storage stability and cure rate. In other instances,
catalyst inhibitor concentrations of up to 500 or more moles of inhibitor
per mole of platinum group metal may be desired. If desired, the optimum
concentration for a particular catalyst inhibitor in a given
photopatternable silicone composition can be readily determined by
routine experimentation. Alternatively, the catalyst inhibitor may be
used at a non-optimum concentration.

[0054] The photopatternable silicone composition can also comprise one or
more additional ingredients, provided the additional ingredient(s)
does/do not adversely affect the photopatterning or cure of the
composition in the method. These additional ingredients are optional.
Examples of additional ingredients include, but are not limited to,
adhesion promoters, solvents (e.g., organic solvents), inorganic fillers,
photosensitizers, and surfactants.

[0055] For example, the photopatternable silicone composition can further
comprise a quantity of at least one organic solvent to lower the
viscosity of the composition and facilitate the preparation, handling,
and application of the composition. Examples of suitable solvents
include, but are not limited to, saturated hydrocarbons having from 1 to
about 20 carbon atoms; aromatic hydrocarbons such as xylenes and
mesitylene; mineral spirits; halohydrocarbons; esters; ketones; silicone
fluids such as linear, branched, and cyclic polydimethylsiloxanes; and
combinations of such solvents. The optimum concentration of a particular
organic solvent in the photopatternable silicone composition can be
readily determined by routine experimentation. The organic solvent may be
removed (e.g., by an evaporative method) from the photopatternable
silicone composition before curing thereof.

[0056] The photopatternable silicone composition can be a one-part
composition comprising components (A) through (C) in a single part or,
alternatively, a multi-part composition comprising components (A) through
(C) in two or more parts. In a multi-part composition, all of components
(A), (B), and (C) are typically not present in the same part unless an
inhibitor is also present. For example, a multi-part silicone composition
can comprise a first part containing a portion of component (A) and a
portion of component (B) and a second part containing the remaining
portion of component (A) and all of component (C).

[0057] The one-part photopatternable silicone composition is typically
prepared by combining components (A) through (C) and any optional
additional ingredients in the desired proportions at ambient temperature
with or without the aid of a solvent, which is described above. Although
the order of addition of the various components is not critical if the
silicone composition is to be used immediately, the hydrosilylation
catalyst may be added last at a temperature below about 30.degree. C. to
prevent premature curing of the composition. Also, the multi-part
silicone composition can be prepared by combining the particular
components designated for each part, and then just prior to use the parts
of the multi-part composition may be combined together.

[0058] A layer of the photopatternable silicone composition may be applied
to a surface of a wafer, and the applied composition may be cured as
described herein to give the cured layer. The cured layer is a product of
photopatterning and curing a layer of a photopatternable silicone
composition comprising components (A), (B) and (C). A plurality of
apertures may be formed in the cured layer on the wafer. The plurality of
apertures in the cured layer formed on the surface of the wafer may be
filled with thermally conductive material to form a thermally conductive
interposer on the wafer, wherein the thermally conductive interposer
comprises a plurality of plugs of the thermally conductive material
disposed in the apertures in a matrix comprising the cured layer defining
the apertures. Typically, a mixture of the photopatternable silicone
composition and a solvent is applied to the surface of the wafer to form
an applied layer covering at least a portion of the surface of the wafer;
photopatterning the applied layer; and curing the photopatterned applied
layer. A portion of the applied layer is irradiated with radiation,
including an i-line radiation, while another portion of the applied layer
is masked, to produce a photopatterned layer, which is a partially
irradiated layer having non-irradiated regions covering at least a
portion of the surface of the wafer and irradiated regions covering the
remainder of the surface of the wafer. The partially irradiated layer is
then partially cured/baked by heat in what the art generally calls a
"soft bake" step. The non-irradiated regions of the partially cured layer
are then removed with a developing solvent to form a partially cured
layer with a plurality of apertures defined therein. The partially cured
layer is then cured to form a cured layer having a plurality of apertures
therein. Typically, the thickness of the cured layer corresponds to a
z-axis thickness and the apertures are formed through the cured layer
along the z-axis thickness. As used herein, when referring to a material
the term "layer" means a shape of the material that is restricted in one
dimension, as for a coating, film or sheet. The dimension is typically
referred to as thickness or height of the layer. The layer may define
first and second major surfaces of the material that may be generally
planar or contoured, e.g., as with a conformal coating topography having
heights of up to a few micrometers. When referring to a layer, the phrase
"along the z-axis thickness" means any direction through the height of
the layer that is generally from any location at the first major surface
of the layer to any location at the second major surface of the layer, or
the vice versa direction. The direction of travel through the height of
the layer may be graphically depicted as a ray through the thickness of
the layer. The direction of travel includes rays having any angle
relative to the first and second major surfaces of the layer, including
right angles, which are (approximately) perpendicular to the first and
second major surfaces, and acute and obtuse angles, which are
non-perpendicular thereto. In some aspects at least some of the apertures
are z-axis vias. The thermally conductive material may be inserted into
the apertures in the cured layer to fill the apertures and give the
thermally conductive interposer. In this aspect the thermally conductive
interposer is prepared on the wafer by a type of process that may be
referred to generally in the art as a "wafer level" process.

[0059] The wafer typically comprises semiconductor material including, but
not limited to, silicon and gallium arsenide. The surface of the wafer
comprises a plurality of integrated circuits including, but not limited
to, DRAM, Flash memory, SRAM and Logic devices. The wafer further
comprises dicing streets or scribe lines, along which the wafer can be
sawed into individual wafers/chips to make semiconductor packages
comprising individual wafers with the thermally conductive interposer
formed thereon. Methods of fabricating integrated circuits and dicing
(saw) streets on wafers are well known in the art. The semiconductor
packages may be combined with additional elements such as a heat sink
and/or a substrate to form semiconductor package devices.

[0060] FIG. 1 shows a semiconductor packaged device (10) wherein the
z-axis thermally conductive interposer (11) with the conductive material
(16) therein, covering the wafer/chip (12), is the heat transport medium
for transferring heat from the wafer (12) to the heat sink (13). The
wafer/chip is bonded to a substrate (15) by a layer of solder (14) placed
between the wafer (12) and the substrate (15) with air-gap (17) in the
remainder of the space between the wafer (12) and the substrate (15).

[0061] The aforementioned method of forming the thermally conductive
interposer is carried out in accordance with an exemplary embodiment
described herein below and shown in FIG. 2. In FIG. 2: [0062] 1) In a
step A the photopatternable silicone (PPS) composition along with a
solvent is deposited on a surface, typically a back surface or a front
surface, of a wafer (12) by conventional coating methods such as spin
coating, spray coating, doctor blading or draw bar coating to produce an
applied layer (18) of thin film of thickness ranging from 5 .mu.m to 50
.mu.m with a thickness variation .ltoreq.2% depending on the wafer size.
Additionally, solder balls (14) are dispensed at pre-determined locations
on the surface of wafer not having the PPS composition deposited thereon,
to enable the wafer to be electrically connected to a substrate (15). The
applied layer is then heated on a hot plate or in an oven between 50
degrees Celsius (.degree. C.) to 130.degree. C. for 2 to 5 minutes to
remove any excess solvent present in the applied layer. The heated wafer
(12) is then cooled to room temperature. [0063] 2) In a step B a portion
of the applied layer (18) is irradiated with radiation including an
i-line radiation, wherein the intensity of Ultraviolet (UV) light is
between 800 mJ/cm.sup.2 to 2800 mJ/cm.sup.2, but typically between 800
mJ/cm.sup.2 to 1400 mJ/cm.sup.2, to produce a partially irradiated layer
having non-irradiated regions (19) which are soluble to solvents and
cover at least a portion of the surface of the wafer (12) and irradiated
regions (20) covering the remainder of the surface of the wafer (12)
where cross linking is initiated. The UV radiated layer is then partially
cured/baked by placing the layer on a hot plate or oven between
100.degree. C. and 150.degree. C. for 2 to 5 minutes to make the areas
exposed to UV become substantially insoluble to developing solvent. The
term "substantially insoluble" means that the irradiated regions of the
partially irradiated layer are not removed by dissolution in a developing
solvent to the extent that the underlying surface of the wafer is
irradiated. The term "soluble" means that the non-irradiated regions of
the partially irradiated layer are removed by dissolution in a developing
solvent, exposing the underlying surface of the wafer. [0064] 3) In a
step C the wafer (12) is developed with developing solvents including,
but not limited to, butyl acetate, mesitylene, and the like, by puddle,
spray or immersion development for 2 to 5 minutes which removes the
non-irradiated layer (19) thereby producing z-axis apertures/vias (21)
with openings from 5 .mu.m to 200 .mu.m dependent on the bond line
thickness. The solvent developed wafer (12) is then dried in the
conventional spin-rinse-dryer system or a spin coater. The dried wafer is
then placed in an oxygen oven for curing temperatures of 250.degree. C.
or less or in a nitrogen oven for curing temperatures ranging from
250.degree. C. to 400.degree. C. between 30 minutes to 3 hours. [0065] 4)
In a step D the apertures/vias (21) are then filled with thermally
conductive material (16) including, but not limited to, titanium,
aluminum, nickel, copper or a combination thereof by conventional
deposition methods such as evaporation or sputtering to form the z-axis
thermally conductive interposer (11) on the wafer (12). The metal filled
apertures provide paths of high thermal conductivity with well controlled
bond line thickness to dissipate heat from the wafer. [0066] 5) In a step
E a thin layer of low melting point solder (22) is then dispensed on the
thermally conductive interposer for attaching a heat sink thereon. The
solder is made from metals or their alloys including, but not limited to,
indium, bismuth, indium-tin alloy, and the like.

[0067] The aforementioned exemplary embodiment is further extended to make
a semiconductor package, wherein in FIG. 2, [0068] 6) in a step F the
wafer (12) is then diced along the dicing (saw) streets to produce
integrated circuit (IC) wafers/chips (23) having the thermally conductive
interposer with z-axis thermal apertures/vias and the layer of solder
thereon. The side having the thermally conductive interposer with the
z-axis thermal apertures and the layer of solder is then placed facing a
semiconductor package lid/heat sink or adjacent to another wafer/chip to
which it needs to be attached. The solder is then melted in a
conventional reflow oven or hot plate to form a bond between thermally
conductive material in the z-axis thermal apertures and the heat sink
(13) to give the semiconductor packaged device (10).

[0069] Additionally, the apertures/vias can be filled with a conductive
paste including, but not limited to, silver, gold, or carbon paste by
drop-on-demand process of an ink-jet printer as known by one skilled in
the art. Furthermore, boron nitride and/or carbon nanotube pillars and
the like, can also be placed in the apertures as thermal contacts.

[0070] Additional exemplary embodiments of the method of forming the
thermally conductive interposer on the semiconductor wafer are provided
herein below to illustrate the invention to one skilled in the art and
should not be interpreted as limiting the scope of the invention. FIG. 5
shows a flow chart depicting steps involved in the method of forming the
thermally conductive interposer in accordance with the additional
exemplary embodiments.

[0071] In FIG. 5, 1: Formation of Z-axis Silicone Vias on a Wafer is done
using an aspect of the method comprising seven steps. A wafer (or other
substrate) and a sample of a photopatternable silicone composition
comprising a composition of vinyl functional silicone resin combined with
a SiH functional polydimethyl siloxane and platinum catalyst are
provided. In a first step of the method, the sample is deposited onto the
wafer (or the other substrate) by spin coating at 2000 RPM (Revolutions
per Minute) for 20 seconds to obtain a 10 micron thick film or layer with
a uniformity of 2-3% across the wafer. In a second step, the coated wafer
from the first step is then heated on a hot plate at 110.degree. C. for 2
minutes in air. The second step is an example of a type of step that is
generally referred to in the art as a "soft bake." In a third step, the
soft baked coated wafer from the second step is then placed on a UV
exposure tool with a mask which allows for the patterning of the soft
baked layer and eventually the location and creation of apertures or vias
therein. The resulting masked coated wafer is then exposed to UV
radiation with an exposure dose of 1000 mJ/cm.sup.2. In a fourth step the
UV exposed coated wafer from the third step is placed on a hot plate at
145.degree. C. for 2 minutes. The fourth step is an example of a type of
step that is generally referred to in the art as a "hard bake." In a
fifth step the hard baked coated wafer from the fourth step is then
placed on a spin coater and butyl acetate as the developer solvent is
dispensed on the hard baked coating. The resulting coated wafer is
allowed to soak with the developer solvent for 2 minutes, and then is
spin rinsed with butyl acetate and finally dried by spinning the
resulting developed coated wafer at 2000 RPM for 30 seconds. The fifth
step solvent develops the hard baked coated wafer, opening apertures such
as vias in the coating. In a sixth step the developed coated wafer having
apertures is then cured in a nitrogen oven at 250.degree. C. for 3 hours
to complete the curing of the developed coating. This results in a coated
wafer with a patterned aperture (e.g., via) structure in/on the cured
layer formed by curing a photopatternable silicone composition according
to the method. In seventh step a thermally conductive filler is deposited
into the apertures (e.g., vias) in the cured layer to fill the apertures
(e.g., vias) and produce the thermal interposer layer on the wafer. An
embodiment of the semiconductor package comprises the thermal interposer
layer disposed on the wafer.

[0072] In an alternative aspect of the method, 2: Formation of Low Stress
Thin Film Layers. A sample is prepared by spin coating a photopatternable
silicone composition comprising a composition of vinyl functional
silicone resin combined with a SiH functional polydimethyl siloxane and
platinum catalyst. The sample is spin coated onto a wafer at 2000 RPM for
20 seconds to obtain a 40 micron thick film with a uniformity of 2-3%
across the wafer. The sample is then heated on a hot plate at 110.degree.
C. for 2 minutes in air. The sample is then placed on a UV exposure tool
and blanket exposed to UV radiation with an exposure dose of 1000
mJ/cm.sup.2 to initiate polymerization across the entire film. The sample
is then hard baked at 300.degree. C. in a nitrogen oven to complete
curing of the sample to a cured layer. The sample is then placed in a
flexus chamber and thermal cycled between room temperature and
300.degree. C. in the nitrogen environment with the stress measurement.
The resulting measured stress as a result of the spin-on silicone is
<2 MPa.

[0073] In an alternative aspect of the method, 3: Photopatternable
silicone (PPS) with Thermally conductive Z-axis Silver Filled Vias. A
sample is prepared by spin coating a photopatternable silicone
composition comprising a composition of vinyl functional silicone resin
combined with a SiH functional polydimethyl siloxane and platinum
catalyst. The sample is spin coated onto a wafer at 2000 RPM (Revolutions
per Minute) for 20 seconds to obtain a 10 micron thick film with a
uniformity of 2-3% across the wafer. The sample is then heated on a hot
plate at 110.degree. C. for 2 minutes in air. The sample is then placed
on a UV exposure tool with a mask which allows for the creation of vias.
The sample is then exposed to UV radiation with an exposure dose of 1000
mJ/cm.sup.2 and then placed on a hot plate at 145.degree. C. for 2
minutes. The sample is then placed on a spin coater and butyl acetate is
dispensed on the sample as the developer solvent. The sample is allowed
to soak for 2 minutes and then spin rinsed with butyl acetate and finally
dried by spinning the wafer at 2000 RPM for 30 seconds. The sample is
then cured in a nitrogen oven at 250.degree. C. for 3 hours to complete
the curing of the sample to a cured layer. The vias were then filled with
conductive silver paste which was dispensed by pipettes. The paste fills
the vias successfully forming z-axis thermal vias. FIGS. 3a to 3f show
microscopic images of the sample, wherein FIG. 3a shows the sample having
40 .mu.m line spaces (31), FIG. 3b shows the sample having 50 .mu.m line
spaces (32), FIG. 3c shows the sample having 100 .mu.m via (33), FIG. 3d
shows the sample having 40 .mu.m via (34), FIG. 3e shows the sample
having silver filled z-axis vias (35), and FIG. 3f shows pattern analysis
of the different vias in the sample.

[0074] In an alternative aspect of the method, 4: Photopatternable
silicone (PPS) with Thermally conductive Z-axis Titanium (Ti) & Aluminum
(Al) Filled Vias. A sample is prepared by spin coating a photopatternable
silicone composition comprising a composition of vinyl functional
silicone resin combined with a SiH functional polydimethyl siloxane and
platinum catalyst. The sample is spin coated onto a wafer at 2000 RPM for
20 seconds to obtain a 10 micron thick film with a uniformity of 2-3%
across the wafer. The sample is then heated on a hot plate at 110.degree.
C. for 2 minutes in air. The sample is then placed on a UV exposure tool
with a mask which allows for the creation of vias. The sample is then
exposed to UV radiation with an exposure dose of 1000 mJ/cm.sup.2 and
then placed on a hot plate at 145.degree. C. for 2 minutes. The sample is
then placed on a spin coater and butyl acetate is dispensed on the sample
as the developer solvent. The sample is allowed to soak for 2 minutes and
then spin rinsed with butyl acetate and finally dried by spinning the
wafer at 2000 RPM for 30 seconds. The sample is then cured in a nitrogen
oven at 250.degree. C. for 3 hours to complete the curing of the sample
to a cured layer. The sample is then placed in a sputter chamber and Ti
and Al are deposited to fill the vias. Furthermore, bumps are created by
depositing Ti and Al on top of the silicone bumps. FIGS. 4a to 4d show
microscopic images of the sample, wherein FIG. 4a shows the sample having
100 .mu.m Ti and Al via (41), FIG. 4b shows the sample having 100 .mu.m
Ti via (42), FIG. 4c shows the sample having 40 .mu.m Ti coated PPS bumps
(43), and FIG. 4d shows the sample having 75 .mu.m Ti and Al coated PPS
bumps (44).

[0075] Invention embodiments include any one of the following numbered
aspects.

[0076] Aspect 1. A method of forming a thermally conductive interposer on
a wafer, the method comprising the step of filling a plurality of
apertures in a cured layer formed on a surface of the wafer, with a
thermally conductive material to form the thermally conductive
interposer.

[0077] Aspect 2. The method of aspect 1, wherein the thickness of the
cured layer corresponds to a z-axis thickness and the apertures are
through the cured layer along the z-axis thickness.

[0078] Aspect 3. The method of aspect 2, wherein at least some of the
apertures are z-axis vias.

[0079] Aspect 4. The method of aspect 3, wherein the maximum width (i.e.,
diameter) of each z-axis via is from 5 micrometers (.mu.m) to 3
millimeters (mm), alternatively from 5 to <1 mm, alternatively from 5
.mu.m to 200 .mu.m.

[0080] Aspect 5. The method of any one of the aspects 1 to 4, wherein the
cured layer is a product of photopatterning and curing a layer of a
photopatternable silicone composition comprising: an organopolysiloxane
containing an average of at least two silicon-bonded alkenyl groups per
molecule, an organosilicon compound containing an average of at least two
silicon-bonded hydrogen atoms per molecule in a concentration sufficient
to cure the composition, and a catalytic amount of a photoactivated
hydrosilylation catalyst.

[0081] Aspect 6. The method of aspect 5, which includes the step of
applying a mixture of the photopatternable silicone composition and a
solvent to at least one surface of the wafer to form an applied layer
covering at least a portion of the surface of the wafer; photopatterning
the applied layer; and curing the photopatterned applied layer.

[0082] Aspect 7. The method of aspect 6, wherein the photopatternable
silicone composition is applied by a coating method selected from the
group consisting of spin coating, spray coating, doctor blading and draw
bar coating.

[0083] Aspect 8. The method of any one of the aspects 6 and 7, which
includes the steps of: irradiating a portion of the applied layer with a
radiation including an i-line radiation, while masking another portion of
the applied layer, to produce a partially-irradiated layer having
non-irradiated regions covering at least a portion of the surface of the
wafer and irradiated regions covering the remainder of the surface of the
wafer; partially curing the irradiated applied layer by heat; removing
the non-irradiated regions of the partially cured layer with a developing
solvent to form a partially cured layer with a plurality of z-axis
apertures defined therein; and curing the partially cured layer to give
the cured layer. The "irradiated applied layer" means the layer after the
applying and irradiating steps and before the partially curing step.

[0084] Aspect 9. The method of aspect 8, wherein the radiation is
ultraviolet (UV) radiation and intensity of the UV radiation is in the
range from 800 millijoules per square centimeter (mJ/cm.sup.2) to 2800
mJ/cm.sup.2.

[0085] Aspect 10. The method as aspect in aspect 8, wherein the irradiated
applied layer is partially cured by heating the layer to a temperature in
the range from 100.degree. C. to 150.degree. C. for from 2 minutes to 5
minutes.

[0086] Aspect 11. The method of aspect 8, wherein the step of removing the
non-irradiated regions is carried out by immersing the partially cured
layer in the developing solvent selected from the group consisting of
butyl acetate and mesitylene.

[0087] Aspect 12. The method of aspect 8, wherein the partially cured
layer is cured by heating the partially cured layer to a temperature in
the range from 180.degree. C. to 400.degree. C., alternatively from
200.degree. C. to 400.degree. C., alternatively from 250.degree. C. to
400.degree. C., for from 30 minutes to 3 hours. As the temperature
increases, the environment or atmosphere in which the partially cured
layer is heated may be made to be increasingly pure or inert (e.g., the
atmosphere may be air at 180.degree. C. or 200.degree. C. and an argon or
helium at 400.degree. C.

[0088] Aspect 13. The method of aspect 6, further comprising, after the
step of applying the photopatternable silicone composition, the step of
removing at least a portion of the solvent from the applied layer by
heating the applied layer to a temperature in the range from 50.degree.
C. to 130.degree. C. for 2 minutes to 5 minutes.

[0089] Aspect 14. The method of aspect 5, wherein the organopolysiloxane
is an organopolysiloxane resin comprising R.sup.1.sub.3SiO.sup.1/2
siloxane units and SiO.sub.{4/2} siloxane units wherein each R.sup.1 is
independently selected from monovalent hydrocarbon and monovalent
halogenated hydrocarbon groups, and the mole ratio of
R.sup.1.sub.3SiO.sub.1/2 units to SiO.sub.{4/2} units in the
organopolysiloxane resin is from 0.6 to 1.9; wherein the organosilicon
compound is an organohydrogenpolysiloxane; wherein the photoactivated
hydrosilylation catalyst is a platinum(II) .beta.-diketonate; or wherein
the organopolysiloxane is an organopolysiloxane resin comprising
R.sup.1.sub.3SiO.sup.1/2 siloxane units and SiO.sub.{4/2} siloxane units
wherein each R.sup.1 is independently selected from monovalent
hydrocarbon and monovalent halogenated hydrocarbon groups, and the mole
ratio of R.sup.1.sub.3SiO.sub.1/2 units to SiO.sub.{4/2} units in the
organopolysiloxane resin is from 0.6 to 1.9, the organosilicon compound
is an organohydrogenpolysiloxane, and the photoactivated hydrosilylation
catalyst is a platinum(II) .beta.-diketonate.

[0090] Aspect 15. The method of aspect 1, wherein the thickness of the
cured layer is from 5 .mu.m to 50 .mu.m.

[0091] Aspect 16. The method of aspect 1, wherein the thermally conductive
material is selected from the group consisting of titanium; aluminum;
nickel; copper; silver; gold; alloys of any two or more of titanium,
aluminum, nickel, copper, silver, and gold; carbon, boron nitride; carbon
nanotubes; and combinations of any two or more thereof.

[0093] Aspect 18. A thermally conductive interposer for dissipating heat
from a wafer, the interposer covering at least one surface of the wafer,
the interposer is composed of a cured layer having a pattern of a
thermally conductive material disposed at discrete locations therein,
wherein the cured layer is a product of photopatterning and curing a
layer of a photopatternable silicone composition comprising: an
organopolysiloxane containing an average of at least two silicon-bonded
alkenyl groups per molecule, an organosilicon compound containing an
average of at least two silicon-bonded hydrogen atoms per molecule in a
concentration sufficient to cure the composition, and a catalytic amount
of a photoactivated hydrosilylation catalyst; the interposer defining a
plurality of apertures at pre-determined locations within the interposer,
wherein at least some of the apertures having the thermally conductive
material disposed therein.

[0094] Aspect 19. The interposer of aspect 18, wherein the thickness of
the cured layer corresponds to a z-axis thickness and the apertures are
through the cured layer along the z-axis thickness.

[0095] Aspect 20. The interposer of aspect 19, wherein at least some of
the apertures are z-axis vias.

[0096] Aspect 21. A method of making a semiconductor package, the method
comprising the following steps: Filling, with thermally conductive
material a plurality of apertures in a cured layer formed on a surface of
a wafer, to form a thermally conductive interposer on the wafer; dicing
the wafer to produce individual diced wafers with the thermally
conductive interposer formed thereon; placing each diced wafer in the
proximity of a substrate such that the thermally conductive interposer of
each diced wafer faces the substrate; placing a bead or layer of solder
between each filled aperture in the interposer and the substrate; and
melting the solder to form a bond between thermally conductive material
in the aperture and the substrate.

[0097] Aspect 22. The method of aspect 21, wherein the thickness of the
cured layer corresponds to a z-axis thickness and the apertures are
through the cured layer along the z-axis thickness.

[0098] Aspect 23. The method of aspect 22, wherein at least some of the
apertures are z-axis vias.

[0099] Aspect 24. The method of any one of the aspects 21 to 23, wherein
the cured layer is a product of photopatterning and curing a layer of a
photopatternable silicone composition comprising: an organopolysiloxane
containing an average of at least two silicon-bonded alkenyl groups per
molecule, an organosilicon compound containing an average of at least two
silicon-bonded hydrogen atoms per molecule in a concentration sufficient
to cure the composition, and a catalytic amount of a photoactivated
hydrosilylation catalyst.

[0100] Aspect 25. The method of aspect 24, which includes the step of
applying the photopatternable silicone composition along with a solvent
to at least one surface of the wafer to form an applied layer covering at
least a portion of the surface of the wafer.

[0101] Aspect 26. The method of aspect 25, wherein the photopatternable
silicone composition is applied by a coating method selected from the
group consisting of spin coating, spray coating, doctor blading and draw
bar coating.

[0102] Aspect 27. The method of any one of the aspects 25 and 26, which
includes the steps of: irradiating a portion of the applied layer with a
radiation including an i-line radiation, while masking another portion of
the applied layer, to produce a partially-irradiated layer having
non-irradiated regions covering at least a portion of the surface of the
wafer and irradiated regions covering the remainder of the surface of the
wafer; partially curing the irradiated applied layer by heat; removing
the non-irradiated regions of the partially cured layer with a developing
solvent to form a partially cured layer with a plurality of z-axis
apertures defined therein; and curing the partially cured layer to give
the cured layer.

[0103] Aspect 28. The method of aspect 21, wherein the substrate is
selected from the group consisting of a semiconductor package substrate,
a semiconductor package lid and another wafer.

[0104] Aspect 29. The method of aspect 21, wherein the solder is selected
from the group consisting of indium, bismuth, indium-tin alloy,
indium-bismuth alloy and indium-bismuth-tin alloy.

[0105] Aspect 30. A semiconductor package comprising: a wafer comprising
at least one surface; a thermally conductive interposer covering the
surface of the wafer for dissipating heat from the wafer, the interposer
defining a plurality of apertures defined at pre-determined locations
within the interposer, at least some of the apertures having thermally
conductive material disposed therein, the interposer composed of a cured
layer, wherein the cured layer is a product of photopatterning and curing
a layer of a photopatternable silicone composition comprising: an
organopolysiloxane containing an average of at least two silicon-bonded
alkenyl groups per molecule, an organosilicon compound containing an
average of at least two silicon-bonded hydrogen atoms per molecule in a
concentration sufficient to cure the composition, and a catalytic amount
of a photoactivated hydrosilylation catalyst; a semiconductor package
substrate; and a bead or layer of solder dispensed between each filled
aperture in the interposer and the substrate to form a bond between
thermally conductive material in the aperture and the substrate.

[0106] Aspect 31. The semiconductor package of aspect 30, wherein the
thickness of the cured layer corresponds to a z-axis thickness and the
apertures are through the cured layer along the z-axis thickness.

[0107] Aspect 32. The semiconductor package of aspect 31, wherein at least
some of the apertures are z-axis vias.

[0108] Throughout this disclosure, the word "comprise", and variations
such as "comprises" or "comprising", are open-ended and will be
understood to imply the inclusion of a stated element, integer or step,
or group of elements, integers or steps, but not the exclusion of any
other element, integer or step, or group of elements, integers or steps.

[0109] The use of the expression "at least" or "at least one" suggests the
use of one or more elements or ingredients or quantities, as the use may
be in the different embodiments of the invention, and may achieve one or
more of the desired objects or results.

[0110] Any discussion of documents, acts, materials, devices, articles or
the like that has been included in this specification is solely for the
purpose of providing a context for the invention. It is not to be taken
as an admission that any or all of these matters form part of the prior
art base or were common general knowledge in the field relevant to the
invention as it existed anywhere before the priority date of this
application.

[0111] The numerical values mentioned for the various physical parameters,
dimensions or quantities are only approximations and it is envisaged that
the values higher/lower than the numerical values assigned to the
parameters, dimensions or quantities fall within the scope of the
invention, unless there is a statement in the specification specific to
the contrary.

[0112] Wherever a range of values is specified, a value up to 10%,
alternatively up to 5%, alternatively up to 1% below and above the lowest
and highest numerical value respectively, of the specified range, is
included in the scope of the disclosure.

[0113] The foregoing description of the specific embodiments will so fully
reveal the general nature of the embodiments herein that others can, by
applying current knowledge, readily modify and/or adapt for various
applications such specific embodiments without departing from the generic
concept, and, therefore, such adaptations and modifications should and
are intended to be comprehended within the meaning and range of
equivalents of the disclosed embodiments. It is to be understood that the
phraseology or terminology employed herein is for the purpose of
description and not of limitation. Therefore, while embodiments herein
have been described, those skilled in the art will recognize that the
embodiments herein can be practiced with modification within the spirit
and scope of the embodiments as described herein.